Federal authorities are investigating the death of Nex Benedict, a 16-year-old nonbinary high school sophomore, who died in February — a day after they were assaulted by three girls in a high school bathroom in Oklahoma. The U.S. Education Department said Friday it had opened a probe into whether the Owasso Public Schools district “failed to appropriately respond to alleged harassment” faced by Nex. Family members said Nex faced bullying since last year. Their cause of death has yet to be determined.